[Ethereum] Pending transactions for 3 days

Often it will appear in seconds after you transmit it. If you are asking about "pending" transactions from an exchange wallet then it will appear shortly after they actually transmit the transaction to the network

Have a look here Understanding transactions better

Full nodes listen and broadcast transactions. As a full node you receive and can display the pending transactions in your transaction pool. That's what etherscan does. Maybe you can't access it through their API, their choice.

So you can get some of the pending transactions as a node, but you don't get to choose, and most likely some transactions will have been included in a block before they reach you in a pending state.